Method and apparatus for cutting devices from substrates

ABSTRACT

A method and system for cutting a wafer comprising a semiconductor substrate attached to an array of integrated devices includes placing the wafer on a stage such as a movable X-Y stage including a vacuum chuck having a porous mounting surface, and securing the wafer during and after cutting by vacuum pressure through the pores. The wafer is cut by directing UV pulses of laser energy at the substrate using a solid-state laser having controlled polarization. An adhesive membrane can be attached to the separated die to remove them from the mounting surface, or the die can otherwise be removed after cutting from the wafer.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a division of U.S. patent application Ser.No. 10/664,755 entitled METHOD AND APPARATUS FOR CUTTING DEVICES FROMSUBSTRATES, filed 17 Sep. 2003, (now U.S. Pat. No. 6,960,813), which isa continuation-in-part of U.S. patent application Ser. No. 10/288,719,entitled METHOD AND APPARATUS FOR CUTTING DEVICES FROM CONDUCTIVESUBSTRATES SECURED DURING CUTTING BY VACUUM PRESSURE, filed 5 Nov. 2002,(now U.S. Pat. No. 6,806,544), which is incorporated by reference as iffully set forth herein; and which application Ser. No. 10/664,755 isalso a continuation-in-part of U.S. patent application Ser. No.10/384,439, entitled SCRIBING SAPPHIRE SUBSTRATES WITH A SOLID STATE UVLASER, filed 6 Mar. 2003; (now U.S. Pat. No. 6,960,739), which is acontinuation of U.S. patent application Ser. No. 10/208,484, filed 30Jul. 2002, now U.S. Pat. No. 6,580,054 which is incorporated byreference as if fully set forth herein; and which claims the benefit ofU.S. Provisional Application No. 60/387,381, filed 10 Jun. 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and processes used inmanufacturing integrated device die, such as integrated circuits andlaser diodes, including diode lasers formed on substrates. Moreparticularly, the present invention provides for securing wafers havingsubstrates, during the process of cutting the wafers into individualdie, and further provides for securing the die separated from the wafersduring and after the wafer cutting process.

2. Description of Related Art

Sapphire Al₂O₃ is used as a substrate for the growth of Gallium NitrideGaN in commercial laser diode manufacturing systems, and can also act asthe substrate of the finished product. However, the use of sapphiresubstrates introduces certain problems.

For instance, sapphire is an electrical insulator and this causesproblems when it is used as a wafer substrate in the fabrication oflaser diodes. Because it is an insulator, electrical contacts to thediodes are usually placed on the wafer's active surface, and thesecontacts occupy areas that would otherwise be utilized for generationand emission of light.

Efforts have been made to implement laser diodes using GaN with othersubstrates. These approaches typically involve removal of the GaN fromthe sapphire substrate on which it is grown, and then remounting it onanother substrate. Advantages of this approach arise because copper orother metal substrates are excellent heat and electric conductionmaterials. A light emitting diode or laser diode LED with a metalsubstrate can be driven with higher current and yield brighter output.In addition, the device with good electric conduction to the substraterequires only one wire bonding on the active surface, and yields higheroutput. Furthermore, the sapphire substrate used for growth of the GaNmay be reused for reduced cost.

For example, U.S. Pat. No. 6,365,429 teaches a method by which “removalof the sapphire substrate after growth of the laser diode arraystructures simplifies providing electrical contacts to the laser diodearrays and avoids special architectures while allowing a superior heatsink to be attached to the laser diode arrays. The laser diode array maybe attached to a thermally conductive wafer before or after substrateremoval by soldering, thermo-compression bonding or other means.” (col.2 11. 20–28).

However, no known method or tools to dice this type of wafer have beenapplied on a commercial scale.

Present methods of separating a wafer based on a sapphire or crystallinesemiconductor substrate into die involve scribing the wafer after firstadhering the wafer to a flexible sheet, known as “blue tape”. Afterscribing, mechanical pressure is applied to break the wafer along thescribe lines, leaving the die attached to the flexible sheet for theirsubsequent removal.

However, wafers having metal substrates cannot be separated into dieusing scribing techniques. Rather, wafers having a metallic substrate,for example one made of copper, must be cut completely through to obtainseparated die. Cutting completely through the wafer would damage anadhesive sheet attached to the wafer, unless very precise control of thecutting process were possible. Furthermore, if an adhesive sheet is notattached to the wafer prior to cutting the die, in order to avoid thedamage, the separated die would be difficult to handle during and afterthe cutting of the wafer. Thus, there is a need for a method and systemfor securing both the wafer and the separated die during and after thecutting of the wafer.

It is desirable, therefore, to provide a system and method for dicingwafers having semiconductive, conductive or metallic substrates, for usein fabricating die in large volume, in an efficient manner thatmaximizes the die-manufacturing yield. Furthermore, it is desirable thatsuch a system be compact, safe to operate, and low cost.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide forsecuring a substrate to a mounting surface in order to perform thecutting substantially through the substrate, thereby permittingseparation of the substrate into die in accordance with a cuttingpattern. It is a further object of the present invention to provide forsecuring the separated die to the mounting surface, both during andafter the cutting process.

One embodiment of the invention provides a method for dicing a wafer,comprising mounting the wafer on a porous member having a mountingsurface; securing the wafer on the mounting surface by applying suctionto the wafer through pores in the porous member; and dicing the waferinto individual die, the die remaining secured to the mounting surfaceby the applied suction.

The present invention provides a method comprising mounting a waferhaving substrate, and carrying an array of integrated devices, on astage such as a movable X-Y stage further comprising a vacuum chuckprovided with a porous mounting surface. Applying suction through thepores of the mounting surface secures the wafer to the mounting surface.The wafer is cut in one embodiment by directing laser energy at asurface of the wafer using a solid-state laser, to form a plurality ofkerfs substantially through the thickness of the wafer, thereby dicingthe wafer. Cutting a wafer by the present method cuts kerfs through thewafer, the kerfs having a width preferably in the range of 10 to 20microns.

The present invention is suitable for manufacturing blue laser diodesbased on Gallium Nitride structures that have been removed from thesubstrate on which they were grown, and then mounted on a substrate.Substrates include herein metals, semiconductors and other compounds ormaterials that are relatively conductive, especially as compared tosapphire, and provide at least one of superior temperature andelectrical conductivity. The present invention can also be applied tonon-substrates, including sapphire. According to the present invention,greater device density on the wafer, and greater manufacturing yield areachieved, while also reducing the time required for dicing the waferinto individual die. Furthermore, the present invention is based oncompact, low-cost machines, and otherwise reduces the overallmanufacturing costs for such integrated device die.

In accordance with the present invention, the X-Y stage comprises avacuum chuck provided with a thin porous mounting surface. The porousmounting surface in various embodiments comprises a thin paper, plastic,ceramic or metal disk having dense micro pores through which a negativepressure can be applied to a wafer placed in direct contact with themounting surface. Embodiments of the porous member comprise one or moreof porous paper, gas filters, sintered ceramic disks or plates, andsintered metal disks and plates made of various compositions.

Also in accordance with embodiments of the present invention, themounting surface comprises a removable member. The use of a removablemember further permits the ready replacement of the mounting surfacewhen required due to wear or contamination.

The laser energy utilized in some embodiments to cut kerfs in the wafershould have a wavelength highly absorbed in the material of thesubstrate. Further, the wavelength should be selected so that it isabsorbed to a much greater degree in the substrate than in the porousmember, so that when the substrate is cut through and the laser impactsthe porous member, minimal damage is caused to the porous member. Forcopper and similar metal substrates, the wavelength is preferably belowabout 560 nanometers, and more preferably between about 150 in 560nanometers. In addition, energy density, spot size, and pulse durationare established at levels sufficient to cut kerfs completely through thewafer. Control of the system, such as by moving the stage whilemaintaining a stationary beam path for the pulses, causes the pulses tocontact the substrate in a cutting pattern at a rate of motion causingoverlap of successive pulses sufficient to cut through the substrate andother portions of the wafer.

Embodiments of the present invention utilize laser pulses having anenergy density between about 10 and 100 joules per square centimeter, apulse duration between about 10 and 30 nanoseconds, and a spot sizebetween about 5 and 25 microns. The repetition rate for the pulses isgreater than 5 kHz, and preferably ranges from about 10 kHz to 50 kHz orhigher. The stage is moved at a rate of motion causing overlap of thepulses in the amount of 50 to 99 percent. By controlling the pulse rate,the rate of motion of the stage, and the energy density, the depth ofthe cut can be precisely controlled, to provide for cutting through thewafer while minimizing the amount of laser energy reaching the mountingsurface securing the wafer.

In embodiments of the present invention, the solid-state laser comprisesa diode pumped, Q-switched, Nd:YVO₄ laser, including harmonic frequencygenerators such as nonlinear crystals like LBO, so that output of thelaser is provided at one of the second, third, fourth and fifth harmonicfrequencies of the 1064 nanometer line produced by the neodymium doped,solid-state laser. In particular systems, the third harmonic frequencyof about 355 nanometers is provided. In other embodiments, thesolid-state laser comprises a Q-switched, Nd:YAG laser, operating toprovide one of the harmonic frequencies as output.

In embodiments of the invention, the method includes detecting edges ofthe substrate while directing pulses at the substrate in the cuttingpattern. In response to detected edges, the system prevents the pulsesof radiation from being directed beyond the substrate.

Embodiments of the present invention direct the pulses of laserradiation at the backside of the wafer substrate.

Thus, embodiments of the invention include mounting the wafer on thestage, moving the wafer under conditions causing cutting of thesubstrate in a cutting pattern on the backside of the substrate, anddetecting edges of the substrate during the cutting process to preventthe pulses of laser radiation from impacting the mounting surface.

The die defined by a cutting pattern are separated from the wafer by thelaser energy, while the suction applied through the pores of themounting surface continues to secure them substantially in the samelocation they occupied on the mounting surface prior to the cutting. Inone embodiment, an adhesive tape is placed onto the separated die afterdicing the wafer is completed, in order to permit removal of the die asa set, and facilitate their handling for subsequent manufacturing steps.Furthermore, the die separated from the wafer remain adhered to theadhesive tape until removed using a pick and place robot, or othertechnology.

Certain embodiments of the invention further provide for controllingpolarization of the laser pulses with respect to direction of the kerfsin the cutting pattern. The polarization is controlled so that kerfs aremore uniform for kerfs cut parallel to different axes. Uniformity can beimproved by random or circular polarization of the pulses in someembodiments. More preferably, polarization of the pulses is controlledso that the polarization is linear and parallel to the kerfs being cut.Embodiments of the invention provide for control of the polarizationusing a laser with an adjustable polarizer, such as a half wave plate,in the optical path.

The invention also provides a system for cutting wafers having asubstrate which comprises a solid-state laser, as described above, astage having a vacuum chuck with a porous surface adapted to support andmove a substrate, optics directing pulses to impact of substrate mountedon the stage, an edge detection system which detects edges of substratemounted on the stage during movement of the stage, and a control system.The control system in embodiments of the invention comprises a computersystem coupled to the solid-state laser, the stage, and the edgedetection system. The computer is responsive to the edge detectionsystem and parameters set by users to cause the pulses to impact of thesubstrate in a cutting pattern at a rate of motion causing overlap ofsuccessive pulses sufficient to cut kerfs in the substrate. Embodimentsof the invention also include a debris exhaust system coupled with thestage.

Embodiments of the invention include a user interface with logic to setup the cutting pattern, and the operational parameters including pulserepetition rate, stage velocity and energy levels to establish kerfdepth, cutting speed and other characteristics of the process.

Other aspects and advantages of the present invention can be seen onreview of the drawings, the detailed description, and the claims whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a wafer cutting system accordingto the present invention.

FIG. 2 is a perspective view of a compact, portable wafer cutting systemaccording to one embodiment of the present invention.

FIG. 3 is a simplified block diagram including the laser system andoptics for the wafer cutting system of the present invention.

FIG. 4 is a simplified block diagram of the edge detection according toone embodiment of the present invention.

FIG. 5 is a perspective view of the X-Y stage comprising a vacuum chuckhaving a porous mounting surface, and a debris exhaust system, of thewafer cutting system according to one embodiment of the presentinvention.

FIG. 6 is an image of a kerf on a substrate including an array ofintegrated laser diodes according to the present invention.

FIG. 7 is a perspective view of a wafer, the porous member, and thevacuum chuck employed in the wafer cutting system of the presentinvention.

FIG. 8 is a top view of a wafer showing a representative cuttingpattern.

FIG. 9 illustrates a process of applying adhesive flexible tape to thecut wafer, in accordance with one embodiment of the present invention.

FIG. 10 illustrates the array of elements adhered to the adhesive tapeafter removal from the stage of the cutting system.

FIG. 11 is a basic flow chart of a manufacturing method according to thepresent invention.

FIGS. 12A–12C show a relationship between polarization of laser pulsesand scribe line scribing direction for uniform V-shaped grooves.

DETAILED DESCRIPTION

A detailed description of embodiments of the present invention isprovided with reference to FIGS. 1 through 12A–12C.

FIG. 1 is a simplified block diagram of a wafer cutting system accordingto the present invention. In the embodiment shown, wafer 14, including asubstrate and an active layer, is mounted with its active surface facingdownward on movable X-Y stage 15. The stage 15 includes a porous member25 on which the wafer is secured by suction through pores on the surfaceof the porous member. High-intensity UV laser energy is directed at thesubstrate surface of the wafer through UV objective 13. A diode pumped,solid-state laser 10 generates the high-intensity UV and close-to-UVpulses at a repetition rate in the kHz range. In preferred systems, thelaser comprises a Q-switched Nd:YVO₄ medium delivering third harmonicoutput as the stream of laser pulses at a repetition rate greater than10 kHz, with a pulse duration of about 40 nanoseconds. The pulses areprovided using an optical delivery system 11 and turning mirror 12 to anultraviolet objective lens 13, which focuses the pulses on wafer 14.

The wafer 14 is supported on a vacuum chuck on X-Y stage 15. In theembodiment shown, the wafer is supported with its active surface down ona porous member 25 having a mounting surface. A vacuum system appliessuction to wafer 14 through the pores of the mounting surface, therebysecurely holding the wafer to the vacuum chuck while the X-Y stage ismoved beneath the UV objective, to cut the wafer using laser energy, inaccordance with the cutting pattern. A gas debris removing system 16cooperates with a gas exhaust system and vacuum 17 to remove debrisgenerated by the ablation of the substrate and wafer materials.

FIG. 2 is a perspective view of a wafer cutting system in one embodimentof the invention. The X-Y stage 15 and porous member 25 are locatedbeneath microscope 52. The diode pumped solid-state laser is compact andlow-cost so that it is efficiently mounted on a cart as illustrated. Thecomputer and other system electronics are contained on the cart. Thecomputer keyboard 50 is mounted on a keyboard tray, which slides in andout of the cart. A flat-panel display 51 is mounted on a swivel base, sothat it may be folded in during movement and storage of the cart. Thesystem includes a microscope 52, which enables viewing of the waferduring the cutting process. Microscope 52 also serves to deliver thelaser energy used in cutting the wafer. Images generated by the camera22, and graphical user interface tools and other display constructs arepresented to the user using the display 51.

The X/Y stage includes a vacuum chuck having a porous member providing amounting surface at least 2.5 inches in diameter, on a six-inchplatform, for holding a two-inch wafer during alignment and cutting. Theporous member is removable in some embodiments of the invention.Representative vacuum chucks that are adaptable for use in the presentinvention are described in U.S. Pat. No. 4,906,011, entitled VACUUMCHUCK.

In one embodiment, the wafer holding surface of the porous member ismade of sintered ceramic materials. For representative examples of thesesintered ceramic mounting members, the wafer mounting or holding surfacehas pore sizes in a range between 0.15 um and 10 um, with a porosityrange between 25% and 75% by volume.

In other embodiments of the present invention, the wafer holding surfaceof the porous member is made of sintered metallic materials. Forrepresentative examples of these sintered metallic mounting members, thewafer mounting or holding surface has pore sizes in a range between 1 umand 20 um, with a porosity range between 10% and 60% by volume.

In yet other embodiments of the present invention, the wafer holdingsurface of the porous member is made of flexible porous materials, suchas paper or plastic. For these flexible porous mounting members, thepore distribution varies in accordance with the type of porous materialutilized. In some embodiments of the invention, the porous member isdisposable and can be removed and replaced between wafers during thecutting process, at low cost. In one example embodiment, the porousmember comprises a leaf of commercially available lens paper, typicallyused for cleaning optical lenses.

Generally, embodiments of the present invention are provided as asemi-automatic turnkey system using a tabletop laser system and computermounted on a cart. The system provides for manual loading and unloadingof wafers. However, the invention contemplates automated wafer loadingand unloading systems as well. Representative systems are adapted toreceive two inch substrate wafers with die sizes, for example about of250 to 300 square. Smaller and larger die sizes are readily handled. Thewafer thickness ranges from about 80 to 200 microns, for typical laserdiode die. The wafer is manually placed on the stage and secured usingthe suction of the vacuum chuck. Manual alignment of the wafer ispossible using manual stage controls. Software controlled cuttingpatterns are implemented with computer control of the wafer stage, andcontrollable speed in the X- and Y-directions. The system includes aclass one laser system which generates spot sizes less than 20 micronsin operational conditions. A kerf is cut to a depth close to thethickness of the wafer, and more preferably equal to the thickness ofthe wafer. Nitrogen gas is used by the debris removing jet, andevacuated using an exhaust pump. Minimal or no damage is caused to themounting surface because the wavelength of the laser is selected so thatit is not significantly absorbed by the porous member, and because ofthe edge detection process, supporting greater yield in the wafercutting process.

The laser system in a preferred embodiment is an electro-opticallyQ-switched, diode pumped, third harmonic Nd:YVO₄ providing an output at355 nanometers wavelength. The pulses have a TEM₀₀ intensity profilewith 10 to 15 micron, or smaller, diameter at 1/e² peak magnitude spotsize on the target surface. The laser pulse duration is about 40nanoseconds, or less and more preferably between about 30 and 10nanoseconds, for example about 16 nanoseconds.

The basic structure of the laser system is like the commerciallyavailable Acculase SS10 Laser System, by New Wave Research, of Fremont,Calif., which is the assignee of the present invention.

The computer system allows for automated control of the laser and stagemovement for defined cutting patterns, which can be set up using thecomputer. A wafer map and cutting definition function allows setup ofthe cutting pattern including rotation control of the stage. Videooverlay shows live video of the sample within a software-controlledwindow to facilitate set up and monitoring of the process. Control forthe cutting parameters including laser energy, repetition rate and stagespeed are provided via the user interface, giving the operator precisecontrol over the depth and quality of the scribing process. A patternalignment function allows the cutting pattern to be moved in the X-, Y-and orthogonal directions to match the actual wafer location duringsetup.

FIG. 3 is a basic layout of optical path for one embodiment of thecutting system according to the present intention. The optical pathincludes a laser 50, optics delivering the output of the laser to asubstrate 74 mounted on the mounting surface of porous member 78 on thevacuum chuck 75 mounted on an X-stage 76 and Y-stage 77. The porousmember 78 in this embodiment is attached to the vacuum chuck 75. Inother embodiments, the porous member 78 is secured to the vacuum chuckby suction during operation.

The laser includes a resonant cavity defined by high reflector 51 andoutput coupler 59. A beam expander 52, laser medium rod 53, cylindricallens 56, diode array 55, thin film polarizer 56, thin film polarizer 57,and electro-optic Q-switch 58 are included. The diode array is operatedto pump the rod 53 to induce resonance at the 1064 nm line for Nd:YVO₄.The output beam is directed to turning mirror 60 and turning mirror 61through spherical focal lens 62 through nonlinear crystal 63. Thenonlinear crystal 63 produces a second harmonic and passes the secondharmonic along with the primary line through spherical focal lens 64 toa second nonlinear crystal 65. The second nonlinear crystal produces athird harmonic output, among others, which is delivered to turningmirror/filter 66 and turning mirror/filter 67 and half lambda wave plate68. The wave plate 68 is motorized and acts as a controllable polarizerfor the output beam. The wave plate 68 may be used to align thepolarization of the output beam with respect to the cutting direction tomake a kerfs cut by the laser pulses uniform in the X- and Y-directions.The third harmonic output, at a wavelength of about 355 nanometers, isdelivered to optics including turning mirror 69, beam expander 70,turning mirror 71, turning mirror 72 and objective 73 to the substrate74. The objective lens 73 is a 20× lens in this embodiment.

The nonlinear crystal 63 used for second harmonic generation can be madeof a variety of materials, preferably LBO, BBO or KTP. Likewise, thenonlinear crystal 65 used for third or higher harmonic generation can bemade of a plurality of materials, preferably LBO or BBO. In onepreferred system, LBO is utilized for both nonlinear crystals 63 and 65.

FIG. 4 illustrates the edge detection system used in preferredembodiments of the present invention. The system includes a white lightsource 81 which provides light through turning mirror 82 and objectivelens 84 to the substrate 85 on the porous surface 86 of a mountingmedium. Reflected light passes through objective lens 84, turning mirror83, turning mirror 82 and is deflected by turning mirror 87 through aspherical focal lens 88 to a photodetector 89. The photodetector 89 iscoupled with the computer system, and its output indicates edgedetection. The edge of the wafer is detected based on the significantdifference of light contrast between the wafer surface 85 and theholding surface on which the wafer is mounted. The computer system stopsthe motion of the stage upon receipt of the edge detection signal,preventing laser pulses from being directed beyond the surface of thewafer.

FIG. 5 provides a perspective of the stage 100, objective lens 101 anddebris removal jet 102 in one embodiment of the invention. The stage 100includes a vacuum chuck 103 centered on a movable plate 104. The vacuumchuck further comprises porous member 106, having a mounting surface forholding the wafer. A movable plate 104 includes manual adjustment knob105 for the Y-direction and a similar adjustment knob (not shown) forthe X-direction. Also, the movement of the stage is automaticallycontrollable. The jet 102 is arranged to deliver air or nitrogen gasinto the region of the ablation in order to remove debris. A vacuum (notshown) withdraws the gas with the debris from the region of the wafer.

In a representative system, the repetition rate is controllable within arange of 20 to 50 kHz, with a stage speed ranging up to 8 to 10 mm persecond. Other combinations of repetition rate and stage speed will bedeveloped according to the needs of a particular implementation.

FIG. 6 shows a magnified view of a wafer having an array of laser diodesformed thereon. Spaces, or streets, about 35 microns wide are leftbetween the individual laser diodes to allow room for cutting. In FIG.6, kerfs (dark lines within the streets) are machined having a width of10–15 microns, on the top surface for perspective of the relativewidths. In a preferred system, kerfs are cut through from the backsideof the wafer. With the system of the present invention with a spot sizein the range of 10 microns, and the precision available, the streets canbe reduced to 20 or 30 microns in width or less. This significantlyincreases the density of devices that can be made on a single substrateand improves throughput in manufacturing process for the die.

FIG. 7 illustrates the basic process of the present convention. Inparticular, a porous member 202 is secured to a vacuum chuck 203. Thevacuum chuck is coupled via coupling 204 to a source of vacuum suction.The porous member 202 may be secured to the vacuum chuck 203 by thesuction of the vacuum, or may be more securely attached depending on theneeds of the particular implementation. A wafer 201 is placed on theporous member 202, and secured on the porous member by suction throughthe pores in the surface of the porous member during the cuttingoperation. Laser pulses 200 are directed at the wafer 201 for thepurposes of cutting kerfs through the wafer. The wafer 201 comprises alayer of GaN 5 to 10 microns thick and a metal substrate such as copperabout 100 microns thick.

FIG. 8 illustrates a cutting pattern for the kerfs. As can be seen,horizontal kerfs 211 and vertical kerfs 210 are cut in the wafer toseparate individual elements from the wafer. For a typical GaN laserdiode, the elements are rectangles or squares about 250 to 300 micronson a side. Each individual element will include one or more laser diodesin the various embodiment of the invention. Shapes other than square orrectangular may be made as well.

As shown in FIG. 9, the wafer 201 has been secured on the porous member202 by suction supplied by the vacuum chuck 203 and the source of vacuum204. Laser pulses have been applied to cut the wafer 201 into an arrayof individual elements. A flexible adhesive tape 221, known as “bluetape” in the semiconductor manufacturing industry, is applied to a frame220. The frame 220 with the tape 221 is lowered onto the array ofelements which had been cut from the wafer 201. The array of elementsadheres to the adhesive tape 221, the vacuum is reduced or removed, andthe adhesive tape 221, attached to the frame 220 with the array ofelements adhered thereto, are removed from the workstation.

FIG. 10 illustrates a resulting workpiece including the frame 220, withthe flexible tape 221 having an array of individual elements, such aselement 222, adhered thereto. The workpiece of FIG. 10 is then suppliedto a pick and place robot system, where the adhesive tape is stretchedto separate the individual elements, and robot may remove the elementsfor further processing.

The basic manufacturing process is shown in the flowchart of FIG. 11. Asmentioned above, the present invention is particularly applicable tomanufacturing of blue laser diodes based on gallium nitride. The galliumnitride is first grown on a sapphire substrate according to thetechnology known in the art. A layer of gallium nitride is removed fromthe sapphire substrate, and attached to a copper or aluminum substrate,or another relatively substrate as compared to sapphire, or to asemiconductor wafer or die having integrated circuits formed thereon forcooperative functioning with the laser diode. The resulting waferincluding the composite of gallium nitride and a substrate, is placed ona porous surface of a vacuum chuck in a first step of the cuttingprocess (block 300). In a next step, suction is applied to secure thewafer on the porous surface (block 301). The wafer is cut into an arrayof elements, using a laser or other cutting technique (block 302). Aflexible adhesive tape is applied to the array of elements (block 303).The tape is removed with the array of elements adhering thereto, fromthe workstation (block 304). A robot is then used to remove the elementsfrom the tape (block 305). In alternative embodiments, the elements areremoved from the porous surface using a robot, or otherwise, withoutadhesive tape.

FIG. 12A illustrates an UV laser 400 which generates a linearlypolarized output beam on line 401 aligned vertically, for example in theplane of the paper, as indicated by arrow 402. The polarization may beestablished intra-cavity as shown in FIG. 3. Alternative systems mayinclude a polarizer outside the cavity. The pulses proceed to half waveplate 403, which is aligned vertically in a Y-direction, parallel withthe polarization 402. After half wave plate 403, the pulses remainaligned vertically as indicated by arrow 404. The pulses proceed throughfocus lens 405 maintaining vertical polarization as indicated by arrow406. The polarization is aligned with the machining direction of ascribe line 407 parallel with a Y-axis.

FIG. 12B illustrates the layout of FIG. 12A, with like components havingthe same reference numbers. In FIG. 12B, half wave plate 403 is rotated45 degrees relative to the position of FIG. 12A. The rotation of thehalf wave plate 403 causes the polarization of the pulses to rotate 90degrees as indicated by arrow 408, extending for this example into thepaper. The pulses proceed through focus lens 405 maintaining theirpolarization as indicated by arrow 410. The polarization 410 is alignedwith the machining direction of a scribe line 411 parallel with aX-axis.

FIG. 12C illustrates laser polarization direction relative to thecutting or machining direction of the scribe line. Thus, a scribe line415 consists of the sequence of overlapping pulses aligned in a cuttingdirection 416. The laser polarization direction 417 in the preferredsystem is parallel with the cutting direction 416. The alignment ofpolarization parallel with the cutting direction is found to produceuniform V-shaped grooves. The V-shaped grooves allow for more uniformseparation of the die than can be achieved with grooves that are moreU-shaped, or that are less uniform.

The present invention provides a process for manufacturing laser diodedie, and other integrated device die, formed on substrates. Proceduresaccording to embodiments of the invention include the following:

-   -   1) laying out and forming laser diodes in an array on an active        surface of a sapphire substrate, with individual laser diodes        separated by streets having a width less than 40 microns, and        preferably around 25 microns or less;    -   2) removing the sapphire substrate of the wafer from the active        surface having the array of laser diodes;    -   3) attaching an electrically substrate on the wafer, on the        underside of the active surface having the array of laser        diodes;    -   4) placing the wafer having a substrate with the active surface        facing down on the porous mounting surface of the X-Y stage;    -   5) moving the wafer to a home position by controlling the stage    -   6) automatically, or semi-automatically, aligning the wafer        position to coordinates established by the computer setup;    -   7) setting up a cutting pattern based on wafer and die size and        layout parameters;    -   8) automatically, or semi-automatically, setting up the lighting        levels for edge detection;    -   9) setting up stage speed, laser polarization and laser power        for the required cutting depth;    -   8) turning on the debris removing system;    -   9) starting the process of laser cutting based on the cutting        pattern on one line parallel to one axis;    -   10) continuing the process on other lines and axes, while        controlling polarization, until cutting of the wafer is        finished;    -   11) causing the stage to return to an exit position;    -   12) attaching a wafer tape on a metal frame to the cut wafer,        turn off the vacuum, and removing the cut wafer from the chuck;    -   13) cleaning wafer with high-speed air or other gas jet to        remove laser machining induced debris;    -   14) stretch the wafer tape for separation of the die, for their        transport to other mounting apparatus using a pick and place        system.

The procedures outlined above are carried out using the systemsdescribed above, or similar systems.

Accordingly, the present invention provides a significantly improvedwafer cutting process and system for use with substrates. The processand system are low-cost, high yield, and high throughput compared toprior art substrate cutting technologies.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims.

1. A method for cutting a workpiece comprising a substrate formed withsemiconductor material, comprising: placing the substrate on a porousmember having a mounting surface; securing the sustrate on the mountingsurface by applying suction to the substrate through pores in the porousmember; cutting through the substrate using laser energy to formindividual elements, the elements remaining secured to the mountingsurface by the applied suction.
 2. The method of claim 1, wherein thelaser energy has a wavelength that is absorbed to a greater degree bythe workpiece than by the mounting surface.
 3. The method of claim 1,further comprising: reducing the suction to release the elements fromthe mounting surface; and removing the elements from the mountingsurface.
 4. The method of claim 1, further comprising; after saidcutting the substrate, adhering the individual elements to a flexiblesheet; and removing the elements adhered to the flexible sheet from themounting surface.
 5. The method of claim 1, further comprising: aftersaid cutting the substrate, using a robotic device to remove theelements from the mounting surface.
 6. The method of claim 1, whereinthe porous member comprises a rigid plate.
 7. The method of claim 1,wherein the porous member comprises a flexible sheet.
 8. The method ofclaim 1, wherein the porous member comprises paper.
 9. The method ofclaim 1, wherein the porous member comprises plastic.
 10. The method ofclaim 1, wherein the porous member comprises ceramic.
 11. The method ofclaim 1, wherein the porous member comprises metal.
 12. The method ofclaim 1, wherein the substrate comprises a semiconductor wafer having anactive surface, and the active surface is mounted in contact with themounting surface.
 13. The method of claim 1, further comprising;generating said laser energy using a solid state laser.
 14. The methodof claim 1, further comprising; generating said laser energy using asolid state UV laser.
 15. The method of claim 1, further comprising;generating said laser energy using a Q-switched solid state laser.
 16. Amethod for manufacturing laser diodes, comprising: forming an array oflaser diodes on a semiconductor substrate; placing the substrate on amounting surface of a porous member; securing the semiconductorsubstrate on the mounting surface by applying suction through pores inthe porous member; and cutting the semiconductor substrate intoindividual elements using laser energy, the elements remaining securedto the mounting surface by the applied suction.
 17. The method of claim16, wherein said forming includes forming a layer of GaN on a sapphiresubstrate, removing the layer of GaN from the sapphire substrate, andmounting the layer of GaN on the semiconductor substrate.
 18. The methodof claim 16, wherein the laser energy has a wavelength that is absorbedto a greater degree by the semiconductor substrate than by the mountingsurface.
 19. The method of claim 16, further comprising: reducing thesuction to release the elements from the mounting surface; and removingthe elements from the mounting surface.
 20. The method of claim 16,further comprising; after said cutting the semiconductor substrate,adhering the elements to a flexible sheet; and removing the elementsadhered to the flexible sheet from the mounting surface.
 21. The methodof claim 16, further comprising: after said cutting the semiconductorsubstrate, using a robotic device to remove the elements from themounting surface.
 22. The method of claim 16, wherein the porous membercomprises a rigid plate.
 23. The method of claim 16, wherein the porousmember comprises a flexible sheet.
 24. The method of claim 16, whereinthe porous member comprises paper.
 25. The method of claim 16, whereinthe porous member comprises ceramic.
 26. The method of claim 16, whereinthe porous member comprises plastic.
 27. The method of claim 16, whereinthe array is placed in contact with the mounting surface.
 28. The methodof claim 16, further comprising; cutting the substrate using a solidstate laser.
 29. The method of claim 16, further comprising; cutting thesubstrate using a solid state UV laser.
 30. The method of claim 16,further comprising; cutting the substrate using a Q-switched solid statelaser.